Crystallization apparatus



1952 J. A. WEEDMAN CRYSTALLIZATION APPARATUS Filed Aug. 22, 1949 IN VENTOR.

J. A. WEEDMAN BY #MMB A T TORNE KS Patented Oct. 28, 1952 UNITED STATESPATENT OFFICE I 2,615,793 CRYSTAL LIZATION APPARATUS John A. Weedman,Bartlesville, kla., assignor to Phillips Petroleum Company, acorporation of Delaware Application August 22, 1949, Serial No. 111,618

crystallization. In another aspect, it relates to an apparatus foreificiently moving a granular mass of crystallized material through afractional crystallizer.

In the separation of mixtures of compounds by fractionalcrystallization, various types of apparatus have been constructed forestablishing contact between a mass or the crystallized material movingin one direction and a mother liquor moving in the opposite direction.Usually these devices employ a flight conveyor or auger for moving thecrystals. In most horizontal type crystallizers, a higher-meltingfraction is removed from one end, a lower-melting fraction is removedfrom the opposite end and the feed is introduced at an intermediatepoint. The apparatus may be jacketed to abstract heat through the wallsand form crystals in the liquid body, which usually fills the apparatus.The crystals that form in contact with a mother liquor are, ordinarily,the higher-melting fraction. In the case of eutectic mixtures, thecrystals may or may not be the higher-melting component but will be thatcomponent present in excess of the eutectic ratio.

One of the principal difficulties with the devices of the prior art isthat the crystal movers are not efiicient if the ratio of solid toliquid becomes too high. When the amount of solid material is too high,the flights of the conveyors bridge over with crystals and no crystalmovement occurs. It is necessary, if separation is to occur, that thecrystals or solid granular material be continuously moved toward theoutlet for the higher-melting fraction and that the remaining liquor bedisplaced toward the opposite end, where the lower-melting fraction iswithdrawn.

I have discovered a solid-moving device which operates efiiciently inany slurry of crystals in liquid and which does not become bridged overwith the material being crystallized. 'My inven-' tion is particularlyadapted to use in a crystallizer that is totally enclosed and has afreezing section near one end and an adiabatic section through which thecrystals must be moved before reaching the product outlet.

The principal object of my invention is to provide a simple andeflicient apparatus for moving crystals through a liquid-full containerand displacing liquid in the opposite direction.

Another object is to provide a conveyor for use in multi-stagecrystallization apparatus.

Another object is to provide a crystal conveyor for moving the solids ofa slurry to one end of 2 from a study of the following drawings,de'sc'zription and claims. q n Figure 1 is a longitudinal sectional viewof a horizontal type crystallizer showing my crystal conveyor inelevation.

Figure 2 is a cross sectional View of Figure 1 taken along line 2-2.

Figure 3 is a detailed view, part sectional and part elevational, takenalong line 3-3 of Figure 2'.

Figure 4 is a cross sectional view of a ylindri cal crystallizer showinga modification of a crys' tal mover in elevation.

In Figure 1, a reciprocating rod 6 extends through the end wall ofcrystallizer l longitudi nally into said crystallizer.Close-fittin'gpistons 8 are spaced along rod 6 and secured thereto.Stufiing box 9 seals the space around rod 6 ,"which is caused toreciprocate by the movement of crank H and connecting rod [2, which areactuated by a driving means, not shown. A bar l3 is' secured to rod 6and extends transversely to form a stop for the foldable pistons 8. Thereciprocating rod may be made up as a unit or it may be made up insections which are joined together bymeans of couplings as shown at M,Product outlets l6 and I! are at opposite ends of the apparatus and feedinlet I8 is intermediate said ends. Cooling jacket 19 forms a freezingsection on one end and heating jacket 2! forms a melting section on theopposite end. Cylinder 22 and piston 23 communicate with crystallizer 1by means of a pas-' sageway 24 to make possible the maintenance of adesired pressure within said crystallizer;

In Figure 2, the cross sectional wall of crystal-' lizer I is shown,inside of which is a collapsible piston which is made up of a close'-fitting ring 26 which is secured to" reciprocate rod 6 by means ofvertically-extending spokes 21. A pair of semi circular flaps 28 areloosely secured to said vertically-extending spokes by means of loops29. Horizontal bar l3 serves to stop the folding of" In Figure 4, theperforate piston 32, which is secured to reciprocating rod 6, isprovided with flaps 33 which close the large openings through saidpiston.

This devicei is'desig ned'for the purpose ofinio'v ing a mass ofgranular solid through a confined .body of the mother liquor, which is'thereby'Ldisplaced in the direction countercurrent to the movement ofthe crystal This device eliminates- ;the' difiici'llty" resultingfrom-bridging" across the i flights which usually occurs with augers orflight conveyors.

By using thy-apparatus, thecrystal's formed in;

the freezin 'zone are-scraped from the walls'by the rigid outer ring andare pushed forward through the crystallizer by the perforate pistons. Atthe same time, liquid is displaced-in the.opposite direction and flowsthrough the perforations in the piston. On the reverse strokathe fold;able flaps 28 fold forward to form an opening around the sides thereofof considerable size. These flaps are prevented from folding com pletelyinward against the reciprocating rod by stop 13. This prevents the flapsfrom coming to rest on dead center andfailing to open on the forwardstroke.- As the; forward. stroke. begins,

the resistance of the solid in the solutionforces theflaps'back-againststops 3i andtherehyifcrms a; piston again.

The pistons of my device are entirely auto-- matic and open and closefreely with'the motion of the reciprocating rod. My device-is; operableas long asthe mixture in-the crystallizer ismaintained asa slurry. Iftheorystals are melted. and a portion of the melt is caused tofiow.-toward1the freezing end as reflux, my device will be operableunder conditions of complete reflux. If the crystals are not melted inthe apparatus but are removed as solid material, it isobvious that this.removal must occur at the same rate that. the material isdelivered tothe end ofthe apparatus.

Otherwise, there wouldbe a building upeofsolid: material in the end-oftheapparatus which could result in damage to the pistons. Then, as; set

forth hereinbefore, crystals resultingfrom-move-rment throughmyapparatus can. be. melted. in the melting. section and the resulting.melt removed through conduit ['6 as-a liquid, or the crystals can bepartially melted and removed-through. conduit it as a slurry, or thecrystals: can. be-

removed as such withoutmeltingthem.

The perforate piston may be made: ofany foraminousmaterialwhich willpermit theifiow of liquid therethrough. without substantial: resist--ance andatthe same time will retain granular, material. It does noteffect the operation if.

some small crystals do pass through the. piston along with: the liquid.Thesecrystals are. probably impure and' more closely approximate thecomposition of the. liquid than dothe larger crystals. which areretained onthe piston. I; have found that a ZO to 30 mesh, screenisexcellent for this purpose.

The screen forv the flaps is.secured toa reinforcingring which has loopsor eyelets to fit around the vertically extending spokes- The screen maybe secured to the reinforcing ring; by any desired method-but I havefound soldering' to be very convenient. The hinge. action of the loopsaround said spokes must be easy so that the resistance required. toopen. and close the flaps will be negligible.

Insteadof stops 3t, which are soldered to the periphery of the. scraperring 25,.any other con venient method for preventing the. backwardfolding of said flaps may be used.

In the. drawings, my apparatus is shown in a; horizontal position.However, it may be operated in a vertical or inclined position; and insome instances, such positions may be preferable. In operating with thecrystallizer full, or substantially full of slurry, the slurry wouldofier sufiicient resistance to the foldablepistons to cause said pistonsto unfold on the pump stroke and fold on the intake stroke. apparatus isof my. inventionwill be. moreclear-ly demonstrated and understood from.a study of the; following: table.

Table WITHAUGER RatcaniL/mln. P SIliggiQK ercent High-Melting. ProductLow- Low- ;Higli=-- Feed Melting, Feed Melting .Melting; Product -Vol.Product Product Rate percent of'ieed 3508 2:64 0.44 14 46.4 14.5 :3v 2.77 2.51 0.26. 9.0 463-2 14:0 87.54 6 3 6.0 0.3 4.8 59.5 v 18.5 90.10. 61 (1.0 0.1 116 r 56.2 24:6 9820 WITH: POROUS E FIS'IZONS" 18.30 14.04.30' 23.5 75.8 55.9 QQLZ 1 24.6 18.9 5.7 23.2 75:9 6352 9859 35.0 23.3=ll.70. 33.5 ;73.9 r 5331 99:

EXAMPLE The following tests were carried out to determine the maximumamount of high purity benzene to. be obtainedv by. crystallization.from. a benzene, n-heptane. feed in. a. crystallizer using, first an.auger-type. conveyor, and; then. a porous. pistonl-type conveyor, suchasthat showninl ig ures.1,,2.; andiBl. Thecrystallizer tubewasa 101 footsection of inch tubing witha coolingjacket adjacent one end'and' aheater at the opposite end.

In the first testsit was. found that the augfir.

. conveyor wouldnotoperateifthe amount of'crystals in the mixtureexceeded about per. cent of the mixture. The output ofhigh-melting,prodiuct (benzene). dropped off rapidly. as. th purity. ofthe product increased. At .98 percentpuritm, Whichis notliigh enough,the high-melting prodnot was 1.6.volume per centof'the feed; which. isa. negligiblequantity for such a process. From. these results, it isobvious; that thecrystallizer was being operated atabout themaximumoutput for the purity of the product.

With. the. porous. piston conveyon. the.- purity of. the highrmeltingproduct was appreciably, higher than that obtained with. they auger.con..-- veyor. The rat'eof output of the high-melting. product increasedas the feedrat'e. wasincreasedl. Evenat a 33.5 volume per cent; output,the. puritit remained at 99 per cent,.which is. considerably.

'better than the 98 per cent purity obtainedat;a.

1.6 volume per cent. output with. the augerrtype conveyor. It. is.believedthat'. the output from. the porous piston crystallizer could.be. increased; evenmore without sacrificing purity of. theprod uct.

The data. in the following tableare. there sults of the tests just.described. Theadvantages If desired, an indicator may be installed inconnection with said flaps to indicate when the.

great-.- Such an indicating device entirely within the scope'of myinvention, which is defined by the following claims.

2 Having described my invention, I claim:

1. A fractional crystallization apparatus. which comprises, incombination, an elongated enclosed container, a product outlet adjacenteach end of 'saidcontainer and a feed inlet intermediate said ends;meansfor adding heat to said container adjacent one end thereof, means forabstracting heatfrom said container along a portion thereof between saidfeed inlet and the unheated end, and: means for moving solid granularmaterial through said container from the cooled to the heated end whichcomprises a reciprocating rod extending axially into said container, aplurality of foldable pistons comprising foraminate members-hinged atspaced intervals to said rod, said foldable pistons being adapted toclose on the intake stroke and open on the pump stroke of said piston;

2. In a crystallizer of the type described comprising an elongatedvessel having a first product outlet conduit in one end portion A ofsaid vessel, a second product outlet conduit in a second end portion Bof said vessel, a feed inlet conduit between said product outletconduits and means for removing heat from said vessel between said feedinlet conduit and said end portion B, an improved solid-conveyor formoving solids toward end portion A which comprises, in combination, areciprocating rod extending axially into said crystallizer,'a pluralityof foldable perforate pistons comprising a screen having a plurality ofperforations disposed at spaced intervals along said rod and securedthereto, and means to prevent rearward folding of said pistons duringthe forward stroke of said rod.

3. In a crystallizer of the type described comprising an elongatedvessel having a first product outlet conduit in one end portion A ofsaid vessel, a second product outlet conduit in a second end portion Bof said vessel, a feed inlet conduit between said product outletconduits and means for removing heat from said vessel between said feedinlet conduit and said end portion B, an improved solid-conveyor formoving solids toward end portion A which comprises, in combination, areciprocating rod extending from one end longitudinally into saidcrystallizer, a plurality of foldable, foraminate pistons disposed atspaced intervals along said rod and secured thereto, means to preventrearward folding of said pistons during the pumping stroke of saidpistons, a rigid band at the periphery of said pistons for scrapingsolidified material from the wall of said crystallizer and means foractuating said reciprocating rod.

4. In a crystallizer comprising an elongated container having productoutlet conduit A and B in the end portions thereof, a feed inlet conduitbetween said outlet conduits, means for abstractingheat from a portionof said container between said outlet conduit B and said feed inletconduit, means for adding heat to a portion of said container betweensaid outlet conduit A and said 6 feed inlet conduitv and means formoving solids therethrough toward outlet conduit A in countercurrentcontact with a liquid, an improved crystal-conveyor which comprises, incombination, a

" reciprocating rod extending axially into said con-' tainer, aplurality of perforate pjstons comprising a screen having a plurality ofperforations secured to-said rods at spaced intervals, a plurality ofopenings through said piston, a corresponding 10 plurality of hingedflaps covering said openings and adapted to open on the intake stroke toallow passage of solids through said openings and to close onthe pumpingstroke to move the solids through said container, and means to effectthe reciprocation of said rod.

5. In a fractional crystallizer comprising anelongated container havingproduct outlet con-- duits A and B in the end portions thereof, a feedinlet conduit between said outlet conduits, means for abstracting heatfrom a portion of said container between said outlet conduit B and saidfeed inlet conduit, means for adding heat to a portion of said containerbetween said outlet conduit A and said feed inlet conduit and means formoving granular solids therethroug-h toward outlet conduit A incountercurrent' contact with a liquid, an improved solid-conveyor whichcomprises, in combination, av reciprocating rod extending longitudinallyinto said container and parallel to the axis of said container, aplurality of pistons formed by paired, semi-circular, flaps comprising ascreen having a plurality of perforations transversely disposed alongsaid rod at spaced intervals and secured thereto, saidfiaps being hingedand rotatable, means to stop the-rotation of said flaps at thetransverse position on the forward stroke and means to stop saidrotation at an angle less than 90 degrees from the transverse positionon the return stroke.

6. In a crystallizer comprising an elongated cylindrical containerhaving product outlet conduits A and B in the end portions thereof, afeed inlet conduit between said outlet conduits, means for abstractingheat from a portion of said container between said outlet conduit B andsaid feed inlet conduit, means for adding heat to a portion of saidcontainer between said outlet conduit A and said feed inlet conduit anda crystal-conveyor for moving crystals toward outlet conduit A, animproved conveyor which comprises, in combination, a reciprocating rodextending axially into said container, a plurality of perforate pistonswhich comprise rings transversely positioned within said cylinder atspaced intervals along said rod, spokes extending inwardly from saidrings and secured to said rod, a pair of semi-circular foraminate flapsrotatably hinged to the spokes of each ring and adapted to assume atransverse position and close the openings within said ring, a boss onthe inner periphery of each ring to stop the rotation of said flaps atthe fully extended position, a forward stop for each pair of flaps whichcomprises a transverse, horizontal bar secured to said rod in frontofthe corresponding piston, and means to actuate said reciprocating rod.

7. In a cylindrical, multi-stage crystallizer having a product outlet ineach end and a feed inlet intermediate said ends, an improved conveyorfor moving granular solids through said crystallizer countercurrently tothe liquid therein which comprises, in combination, a reciprocating rodextending axially into said crystallizer, a plurality of closely-fittingrings transversely positioned within said crystallizer at spacedintervals along said: 110d: andisecuredi thereto by means trans= verse;ba'fs extending: outwardly-from saith rod; a: cornesponding: plurality.of; paired; semiecimular; ioraminato; flaps rotate-lilysecured along:theisnonecircular edges to said: transversebarsg meanst tcwstion saidfiapsettheinfulhzextendedr position; and meanstoactuatesaintreciproeating rod;

8; In. a fractional cliystailizerwhich comprises elongated: container"having product: outlet eonduitsA: and: BE in the end portions thereof;we feedinlet conduit between. said; outlet; conduits;meanszforabstracting heatfromta portionzofisaid; containen betweensaidioutletrconduittB- anciisaitf feed inlet conduit, meansfor adding.heat: to; a" portion of said container between saidoutletcorrduit A andsaid feed inletconduit? and as crystalconveyon for; movingcnystalstowardi outlet. conduit A, animgroved conveyor which: comprises:a;

reciprocatingrodextending axially 'intozsaid comtainen; av -plurality ofperiorate,-.pistons-comnrise ing; a screenhevinge, plurality ofperforationsidisposed; along and: foldably; securedto said rod;- meansto-stop the unfolding; ofsaid. piston-s at their fully extended-positionduring; the: advance stroke OfzSSid rod, endmeans: to. actuatesaidfrod;

9; In a-.multi-sta ge:orysta,l1izen comprising a: cylinderhaving aproduct outlet-in each end. and aaieed fillet-intermediate said: ends,an improved: cr'ysta-lnonveyor which comprises; inecombination; a'eeiprocating rod-extending through said cy1in der and. parallel to theaxis" of said cylinder-r, a; pluralityof perforate pistons disposedalong;Saidv rod: and foldablysecured thereto; s-aidi pistons comprisingpaired, semi=circulan foraminate Nil members hinged: to rotate about-a vcommon. axis 35 83 of saidhinged: members: aboutzsaid axis: at: theiri111!yxmened position 011217116 forward strokeiof thee.

rodimeanstostontherotation ofsaidsemieciroullarmembers on'the: reversestroke; short ofa deade center-.positiomendmeansW cause said mite.-

reciprocate;

10:12 frwctionaicrystallization. apparatus whiclncomprises incombination, anze-longatedien closed oontainen, a; product outlet.adjacenteachx ondi of said' containersuch a. feed; inlet; inter-mes;diate said ends, means for adding: heat: twsaidi containeradjacent.-one; end: thereof; means: for abstracting,heatfromisaidflcontainet alongapertion; thereof between said feed; inlet. and-1 thez-une heated end;,andmeans for moving: solid grams Ian material: through said; eontainenfrom; the coo'l'edtorthewheatedf end which :compniseseueeimmcating; rod;extending: serially: into. said con;-r tainenga: pluralityofperforatmpistons secureditm said= rod; and spacedl intervals; each:of:' said pistol-1s;- comprising, a; plurality: ofi' perforate membersadapted to open: to permit passage of throughsaid pistonsand-adantedxtooloseso asto. movesolids through said: containers-m1 thedireee tion of the heated end;-

I REFERENCES GITED, The following references are of record in the fileof "this: patent? UNITED- STAT-ES.

Numben

1. A FRACTIONAL CRYSTALLIZATION APPARATUS WHICH COMPRISES, INCOMBINATION, AN ELONGATED ENCLOSED CONTAINER, A PRODUCT OUTLET ADJACENTEACH END OF SAID CONTAINER AND A FEED INLET INTERMEDIATE SAID ENDS,MEANS FOR ADDING HEAT TO SAID CONTAINER ADJACENT ONE END THEREOF, MEANSFOR ABSTRACTING HEAT FROM SAID CONTAINER ALONG A PORTION THEREOF BETWEENSAID FEED INLET AND THE UNHEATED END, AND MEANS FOR MOVING SOLIDGRANULAR MATERIAL THROUGH SAID CONTAINER FROM THE COOLED TO THE HEATEDEND WHICH COMPRISES A RECIPROCATING ROD EXTENDING AXIALLY INTO SAIDCONTAINER, A PLURALITY OF FOLDABLE PISTONS COMPRISING FORMINATE MEMBERSHINGED AT SPACED INTERVALS TO SAID ROD, SAID FOLDABLE PISTONS BEINGADAPTED TO CLOSE ON THE INTAKE STROKE AND OPEN ON THE PUMP STROKE OFSAID PISTON.